1. Field of the Invention
Lubricating oils are employed not only for lubrication, but as a vehicle to promote the protection of the surfaces lubricated by the oil. The tendency for rusting has required that lubricating oils include additives which inhibit rust. Also included in lubricating oils for internal combustion engines are bases capable of neutralizing the acids formed during fuel combustion or introduced into the oil by blow-by or other mechanisms.
The oxidation of hydrocarbon oils yields a variety of compounds that are deleterious for the service for which the oils are intended. A large variety of end products result from the oxidation. Among those identified are lactones, ketones, aldehydes, esters, alcohols, hydroxy acids, anhydrides, peroxides, and acids. The acidic and peroxidic components attack metals, corrode bearings, and promote wear and rust. Acidic products are also a major source of the oil insolubles that cause ring sticking, sludging, and impede oil flow.
Diesel fuels contain varying amounts of sulfur which is oxidized in combustion and mainly exhausted from the engine. However, appreciable quantities are blown through the ring zone together with air and water. Under these conditions, the SO.sub.2 is converted to SO.sub.3, which in turn is converted to sulfuric acid. This results in acidic attack on the oil, rings and cylinders.
While gasoline fuels are low enough in sulfur content so that sulfuric acid attack should pose no problem, the blow-by of fuel oxidation products and water which accumulate in the crankcase lead to sludging, corrosion and lacquer formation.
The three important mechanisms available for inhibiting rust and corrosion are acid neutralization, inhibition of oil oxidation and protective film formation. Since acids are involved in the rust and corrosion processes, it is obvious that their neutralization will serve as a preventative. This is a function performed by alkaline earth metal carbonates, which when dispersed in a lubricating oil by means of a metal salt dispersant (phenate or sulfonate) will maintain low copper-lead bearing corrosion rates and inhibit rusting as long as the pH of the oil is above 6. Furthermore, it has been shown that in the diesel engine corrosion by sulfuric acid is prevented as long as the pH of the oil is maintained above 4.5. Ring and cylinder wear in gasoline engines operating under low temperature conditions (jacket temperature = 32.degree.C.) increases sharply when the pH of the oil drops below 6 [W. T. Stewart and F. A. Stuart, Advances in Petroleum Chemistry and Refining, Vol. 7, p. 1 (1963)].
Rusting and acidic corrosion also constitute a serious problem in steam turbines and other machinery exposed to moisture. Like the internal combustion engine corrosion discussed previously, this type of corrosive wear is readily controlled by effective alkaline additives.
2. Description of the Prior Art
In U.S. Pat. No. 3,458,444, alkenyl succininates of hydrocarbon-substituted ethanolamines are taught as rust inhibitors. Various alkanolamines are taught in U.S. Pat. Nos. 3,197,510 and 3,398,197, the compounds having a wide variety of uses. Esters of the imidazolines are taught as corrosion inhibitors in U.S. Pat. No. 3,017,352.
U.S. Pat. Nos. 2,681,315 and 2,833,717 teach lubricating oil compositions containing poly(oxyethylene)alkylphenol useful as rust or corrosion-inhibiting additives. U.S. Pat. No. 2,921,027 teaches poly(oxyethylene)sorbitan fatty acid ester as a rust inhibitor. U.S. Pat. Nos. 2,620,302, 2,620,304, and 2,620,305 teach 1,2-poly(oxyalkylene)glycol lubricating compositions. Alkaline earth metal salt dispersants are also mentioned in some of the foregoing patents. U.S. Pat. NO. 3,509,052 teaches the use of succinic acid derivatives in combination with poly(oxyalkylene)polyols and U.S. Pat. No. 3,567,784 is also concerned with the poly(oxyalkylene)polyols.